Numerical modeling of lightning-produced NOx using an explicit lightning scheme: 1. Two-dimensional simulation as a "proof of concept"

Abstract

We use the two-dimensional (2D) version of our Storm Electrification Model to test its potential for studying lightning-produced NOx. We assume that NO production is a function of energy dissipation and calculate this value from the electric field before and after each lightning flash. We use a production rate of 9.2 × 1016 molecules joule-1 to generate the NO. Using a limited set of chemical reactions involving NO, NO2, and O3, we simulated a small storm with 10 intracloud lightning flashes produced over a 2-min span. Their energy dissipation ranged between 0.024 and 0.28 GJ. The simulation was run an additional 18 min after the cessation of lightning. Our results show that the parameterization produced NO mixing ratios internal to the cloud of the order of 10 ppbv after the most energetic flashes and 1-2 ppbv in the upwind portion of the anvil toward the end of the simulation. These mixing ratios are shown to be comparable to observations in a generic sense. Comparison with the C-shaped profiles developed by Pickering et al. [1998], also using a 2D model, show similarities, but our results are more weighted toward larger values at higher altitudes than those of Pickering et al. This may be due to differences in the length of the simulation, a lack of cloud-to-ground lightning in our work, a lack of reactive chemistry in Pickering et al., or the use by Pickering et al, of the assumption of Price et al. [1997] that intracloud flashes dissipate one tenth the energy of cloud-to-ground flashes. We show, using recent observational data and an analysis of the assumptions of Price et al., that this one tenth energy dissipation assumption is not appropriate. We conclude that our use of an explicit lightning scheme to study NO production at the process level is a viable methodology. © 2003 by the American Geophysical Union.